Senile dementia of the Alzhimer's type (SDAT) is studied to differentiate SDAT patients from those with organic disease. Cognitive testing, medical/neurologic assessment, and a computerized tomography (CT) scan are used to evaluate 200 SDAT patients and 100 normal subjects in two age groups, 60 to 70 years old and 71 to 85 years old. The predictive value of CT scan readings in identifying persons prone to further cognitive deterioration is determined by comparing initial test findings with a repeated evaluation 18 months later.